This invention relates to electronic parts for use in a high-frequency circuit parts.
As examples of prior art electronic part for use in a high-frequency circuit, two directional couplers are illustrated in FIGS. 9A, 9B and 10. The prior art directional coupler, shown at 86 in FIGS. 9A and 9B, comprises a dielectric substrate 81, on the front surface of which are formed two mutually opposite meandering coupler lines 82, 83 as an electrode pattern with their ends reaching mutually opposite edges of the dielectric substrate 81. Input/output electrodes 84 are formed on these edges of the dielectric substrate 81, connected to the ends of the coupler lines 82, 83. A grounding electrode 85 is formed on the back surface of the dielectric substrate 81. The coupler lines 82, 83, the input-output electrodes 84 and the grounding electrode 85 may be formed by any thin-film technology such as vapor deposition, sputtering and plating methods. FIG. 10 shows another prior art directional coupler 95 having a multi-layered dielectric substrate 91 and coupler lines 92, 93 formed mutually opposite to each other inside the multi-layered dielectric substrate 91 by a thick-film printing method. Grounding electrodes 94 are formed on both upper and lower surfaces of the multi-layered substrate 91.
In the case of the prior art directional coupler 86 with a high degree of coupling such as a 90.degree. hybrid, however, the coupler lines must be made extremely fine, and hence the film must be made very thin. This has the unfavorable consequence of increasing not only the resistance but also the insertion loss when it is used as a directional coupler. In the case of the prior art directional coupler 95, on the other hand, precision in the measurements of the coupler lines 92, 93 is poor because the lines 92, 93 are formed by a thick-film printing method, and there are large fluctuations in electrical characteristics among the produced parts.